1. Field of the Invention
This invention generally relates to a device and method for displaying a picture and more particularly to a flat panel type color display for use in a color television receiving device, a display terminal of a computer system and so on.
2. Description of the Related Art
A typical example of a conventional image tube is disclosed in the Japanese Patent Application Provisional Publication No. 56-76149 Official Gazette. FIGS. 1(A) and (B) are a section and plan views of this image tube, respectively. As shown in these figures, this image tube is provided with a flat tube body 101 made of glass and so forth. On an inner surface 101a of this tube body 101, a plurality of stripe-like control electrodes 102 [102.sub.1, 102.sub.2, 102.sub.3, . . . 102.sub.n ], the number of which is equal to that of pixels in the horizontal direction thereof, are arranged in parallel with each other at a predetermined interval. Further, on each of the control electrodes 102, a fluorescent screen 104 composing a screen of the display is formed by coating the electrode with fluorescent material 103 suitable for a low velocity electron beam. Over the fluorescent screen 104, is arranged a mesh-like electrode 107 facing the fluorescent screen 104 at a predetermined interval. Further, on another inner surface 101b of the tube body 101 facing the fluorescent screen 104, is provided a main deflecting electrode 106 for deflecting a strip-like electron beam to the fluorescent screen 104 and making the electron beam scan the screen 104 in the vertical direction as indicated by an arrow C in FIG. 1(B).
This main deflecting electrode 106 is made of a transparent conductive film. On the other hand, at the right side of the fluorescent screen 104, as viewed in FIG. 1(A) (that is, in a bottom end in the longitudinal direction of each control electrode 102, as viewed in FIG. 1(B), is arranged a beam source 108 for emitting a strip-like low velocity electron beam 105. The beam source 108 is composed of a cathode 109 stretched in the horizontal direction from left to right as viewed in FIG. (B) and made of tungsten, an electrode 111, to which a voltage substantially equal to a voltage applied to the cathode 109 is applied, enclosing this cathode 109 and having a slit 110 also extending in the horizontal direction from left to right as viewed in this figure and an accelerating electrode 113, to which a positive constant voltage, having a narrow slit 112. Further, in front of the beam source 108, is arranged an auxiliary deflecting electrode 114 comprised of a pair of electrode plates 114A and 114B for deflecting the strip-like electron beam 105 in cooperation with the main deflecting electrode 106.
Next, an operation of the conventional device as above constructed will be described hereinafter.
First, a nonmodulated strip-like electron beam emitted from the beam source 108 in parallel with the fluorescent screen 104 is deflected by the auxiliary deflecting electrode 114 and the main deflecting electrode 106 and is further incident on the fluorescent screen 104, and the fluorescent screen 104 is scanned at a constant speed by varying the extent of the deflection of the electrode beam in the vertical direction indicated by the arrow C in FIG. 1(B).
On the other hand, a video signal of one horizontal scanning interval is simultaneously supplied to each control electrode 102. In this case, the video signal is sampled correspondingly to pixels positioned in the horizontal direction, that is, to the control electrodes 102, and each of the sampled signal is serially supplied to each corresponding control electrode 102. Thus, a video signal is fed to each control electrode every horizontal scanning interval. At that time the surface of a fluorescent layer 103 provided on the each control electrode 102 is irradiated with the strip-like electron beam 105, and parallel lines on the fluorescent screen 104 are serially excited by the scan of the strip-like electron beam 105 and emit light, thereby obtaining a desired image.
However, the conventional device as above constructed has drawbacks that if the resolution power thereof is increased by dividing each control electrode among pixels, with the picture displaying area, which is available for displaying a picture or image, unchanged. A pitch i.c., or interval between adjacent control electrodes becomes extremely small and a division width obtained by the division becomes narrower. In such case there there is a limitation on the withstand voltage applied between control electrodes. The voltage of the video signal applied to each control electrode cannot be sufficiently increased and consequently it becomes very difficult to obtain a light picture. To avoid such problem the number of video signal processing circuits should be equal to that of the control electrodes. Such provision increases power consumption. A further problem is that the angle of incidence of the electron beam to the fluorescent screen varies with the vertical scanning position of the electron beam, and the size of a beam spot in the vertical direction also changes.
In addition, it is to be noted that there occur the reflection of the electron beams and the secondary emission of electrons by the fluorescent screen 104 and the mesh-like electrodes 107 when the electron beams are incident thereon. These reflected and secondary electrons are reflected and emitted at an angle of emission, the magnitude of which is nearly equal to an angle of incidence, to the fluorescent screen 104 and the mesh-like electrodes. Further, these reflected and emitted electrons are deflected by the electric field present between the main deflecting electrode 106 and the mesh-like electrode and are incident once more on positions, which are not the same with the positions of the electron beams at the last incidence. This causes the fluorescent material 103 to unnecessarily emit light at unintended positions on the screen. Thus, the conventional device has another drawback that the contrast is reduced, and a ghost-like image is generated in the vertical direction of the screen of the display. The present invention is accomplished to eliminate the drawbacks of the conventional device.